I have definitely noticed this effect after prolonged bouts of intense coding. There comes a point when the tank is just empty, and I might as well stop because I'll mostly just sit there and stare at the screen. I'm definitely more likely to succumb to easy but bad choices such as fast food at those times too.

A 10 minute nap seems to reset me though, which is cool. I try to take one after completing a good sized chunk of work so I'll be capable of completing another one or two in the same day.